3-D velocity structure of P-wave in the crust and upper-mantle beneath Pamir and adjacent region

We have investigated the three-dimensional seismic velocity structure in the crust and upper mantle down to the depth of 210km beneath Pamir and adjacent regions (30degrees-45degreesN, 65degrees80degreesE) with more than 59,054 P-wave arrival times from 5402 earthquakes recorded by 73 stations, collected from the bulletin of ISC. Travel times and ray paths were calculated with an effcient 3-D ray-tracing technique, and the inversion was conducted by the algorithm LSQR. The involved events and the stations are located within the studying area. We set up 3-D grid nodes with a horizontal spacing of 1degrees x 1degrees and a vertical spacing of about 20-90km. The resolution of the inversion result has been discussed with checkerboard resolution tests, and two parameters have been introduced to quantitatively describe the recovered degree. The preliminary results are as follows: (1) At the depth of 10km beneath Tienshan Mountain, there is a visible higher velocity region at the east and west parts of it, but the lower velocity area in the vicinity of 74degreesE, 41degreesN may be correlated with a larger dislocation of the larger fault in the surface of Tienshan moutain. Near the longitued of 75degreesE of Tienshan, the velocity is a bit higher at the depth of 40-60km and a bit lower at the depth of 60-90km or more, which shows the complexity of the tectonic and material property under the Tienshan Mountain. (2) From the vertical profile of the velocity from south of Pmair knot to north of Tienshan, it shows that near pamir knot there exists an obvious collision between India and Eurasia plate: the plateau is formed by raised ground surface, the shallower crustal strata of slow velocities are subducted into deeper depth.